Catalytic Activity For Ethylene Polymerization Research Articles

Metallocene supported on a polyhedral oligomeric silsesquioxane-modified silica: Structural characterization and catalytic activity for ethylene polymerization

Preliminary results on the activity of metallocene supported over a polyhedral oligomeric silsesquioxane (POSS)-modified silica for ethylene polymerization (Bianchini et al., J Polym Sci Part A: Polym Chem 2005, 43, 5465–5476) were extended showing the effect of large variations of the amount of both POSS and metallocene on the catalyst activity. Diffuse reflectance infrared spectroscopy results showed that at low concentrations (<1 wt %), POSS was physically adsorbed on SiOH groups present in the silica surface through H-bonds. At larger concentrations, POSS was adsorbed by covalent bonds with the silica surface. The metallocene catalyst was adsorbed either on the silica surface by interactions with residual SiOH groups or in the organic branches of the POSS. It was found that the highest contribution to the catalyst activity arose from the metallocene directly adsorbed on the silica support. The effect of POSS to increase the catalyst activity was mainly due to its effect as a horizontal spacer of metallocene molecules adsorbed on the silica surface. An optimum range of POSS and metallocene adsorbed on the silica support was found that gave catalyst activities close to the one of the homogeneous system while doubling the molar mass of the polyethylene produced. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

New binuclear half-titanocene derivatives with aryl-substituted cyclopentadienyl ligands: synthesis, structures, and catalytic properties

Two binuclear oxo-bridged half-titanocene complexes, µ-oxo-bis[(1-aryl-2,3,4,5-tetramethylcyclopentadienyl)dichlorotitanium] [(ArMe4CpTiCl2)2O, Ar = 4- i PrC6H4 (3), 4- t BuC6H4 (4)], have been prepared by the treatment of 1-aryl-2,3,4,5-tetramethylcyclopentadienyltitanium trichloride [ArMe4CpTiCl3, Ar = 4- i PrC6H4 (1), 4- t BuC6H4 (2)] with 0.5 equiv of H2O. Complexes 3 and 4 have been characterized by elemental analysis and 1H- and 13C-NMR (nuclear magnetic resonance; NMR) spectroscopies, and their molecular structures have been determined by X-ray crystallography. When activated with i Bu3Al and Ph3CB(C6F5)4, complexes 3 and 4 both exhibit reasonable catalytic activity for ethylene polymerization (90 × 103 to 280 × 103 kg PE (mol Ti)−1 bar−1 h−1), producing polyethylenes with moderate molecular weight.

Chromium(III) Complexes with Chelating Anilido–Imine Ligands: Synthesis, Structures, and Catalytic Properties for Ethylene Polymerization

AbstractA series of novel chromium complexes that bear anilido–imine ligands, [{ortho‐C6H4(NAr′)(CH=NAr″)}CrCl2(thf)2] [Ar′ = Ar″ = C6H5 (1); Ar′ = Ar″ = p‐MeC6H4 (2); Ar′ = Ar″ = 2,6‐Me2C6H3 (3); Ar′ = 2,6‐iPr2C6H3, Ar″ = 2,6‐Me2C6H3 (4); Ar′ = Ar″ = 2,6‐iPr2C6H3 (5)], have been synthesized and characterized by elemental analysis, IR spectroscopy, and ESI‐MS. The molecular structures of complexes 1 and 2 have been confirmed by single‐crystal X‐ray diffraction analysis. When activated with methylaluminoxane (MAO), these complexes exhibit reasonable to good catalytic activity for ethylene polymerization and produce polyethylene with moderate molecular weights.

An Unsymmetrical Iron(II) Bis(imino)pyridyl Catalyst for Ethylene Polymerization: Effect of a Bulky Ortho Substituent on the Thermostability and Molecular Weight of Polyethylene

Three new iron(II) 2,6-bis(imino)pyridyl complexes bearing bulky and unsymmetrical substituted aniline groups, [2-(CH(CH3)(C6H5))-4-R1-6-R2-C6H2N═C(CH3)]2C5H3NFeCl2 (1, R1 = H, R2 = methyl; 2, R1 = methyl, R2 = methyl; 3, R1 = H, R2 = methoxy), were synthesized. The unsymmetrical bis(imino)pyridyl ligand L2 contains three isomers that can be detected by 1H NMR and 13C NMR spectroscopy. However, the corresponding complex 2 exhibits only one isomer in solution. X-ray diffraction of 2 confirms that the iron complex adopts a Cs configuration. These complexes activated by methylaluminoxane (MAO) have high catalytic activities for ethylene polymerization and produce linear polyethylenes with bimodal or broad molecular weight distribution. The steric and electronic effects of the ortho substituents on the aniline moiety distinctly affect the molecular weight of the obtained polyethylene. In comparison with 1 and 3, having a single ortho substituent on the aryl rings, and the typical complex 4, containing o-diiso...

Synthesis of a new salphen‐type titanium complex and its application in ethylene polymerization and copolymerization

AbstractTiCl2[salphen(di‐tBu)] was synthesized, characterized and employed as pre‐catalyst in ethylene homo‐ and copolymerization with propylene, 1‐octene and 10‐undecen‐1‐ol. X‐ray diffraction study on the titanium complex revealed a distorted octahedral coordination of the central metal with a trans‐Cl, cis‐O, cis‐N arrangement. The complex combined with MAO afforded moderate catalytic activities in ethylene polymerization. Furthermore the catalyst not only copolymerized ethylene with apolar monomer (propylene and 1‐octene), but also possessed significant capability of incorporation with polar monomer (10‐undecen‐1‐ol). Only single insertion of 1‐octene unit in ethylene‐co‐1‐octene polymer was detected by 13C NMR spectrum. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Supporting of nickel(II) acenaphthenediimine with free amino group for ethylene polymerization

Bis (4-(4-amino-3, 5-diethylbenzyl)-2, 6-diethylphenylimino) acenaphthene] dichloronickel (NiLCl2) was prepared and supported on SiO2 modified by methyl trichlorsilane(S-1) and on SiO2-MgCl2/TiCl4 (S-2) respectively. Two supported catalysts S-1 and S-2 used as catalysts for ethylene polymerization were studied and the influences of various polymerization conditions, including the polymerization temperature, cocatalysts, Al/Ni molar ratio on the catalytic activity, branching degree and branch length of PE were also investigated. The experimental results show that the supported catalysts exhibit higher catalytic activity for ethylene polymerization, the highest catalytic activity of S-1 using AlEt2Cl as cocatalyst at 50°C, reaching 5.8×105gPE/molNi··h, and needed lower Al/Ni molar ratio compared to homogeneous analogue.

Synthesis, structures and ethylene polymerization behavior of half-metallocene chromium(iii) catalysts bearing salicylaldiminato ligands

A series of half-metallocene chromium(III) complexes bearing a salicylaldiminato ligand, Cp′[2-R1-4-R2-6-(CH = NR3)C6H2O]CrCl [Cp′ = Cp (1, 5), Cp* (2, 3, 4, 6, 7, 8); R1 = Ph (1, 2, 3, 5, 6, 8), iPr (4), tBu (7); R2 = H (1, 2, 3), Br (4), NO2 (5, 6, 7, 8); R3 = iPr (1, 2, 5, 6, 7), tBu (3, 4, 8)], were synthesized. The structures of complexes 1, 3–5, 7–8 were determined by single crystal X-ray diffraction analysis. The X-ray crystallographic analysis indicates that these complexes adopt a pseudo-octahedral coordination environment with a three-legged piano stool geometry. Upon activation with a small amount of AlEt3, complexes 1–8 exhibit good to high catalytic activity for ethylene polymerization and produce ultra-high molecular weight polyethylene (PE) under mild conditions. The productivity of these complexes is relatively low when activated with AlMe3 and AliBu3. Both the productivity of these catalyst systems and the molecular weight of the produced PE can be tuned in a broad range by changing the ligands and the AlR3 co-catalyst.

Heterogeneous Polymerization of Ethylene and 1‐Hexene with Me3SiCp2ZrH3AlH2/SiO2 Activated with MAO

AbstractThe aluminohydride of zirconocene Me3SiCp2ZrH3AlH2 was supported on pre‐treated SiO2, and its catalytic activity for ethylene polymerization and ethylene‐1‐hexene copolymerization was evaluated in order to compare with the corresponding activity of the complex in solution. As expected for systems based on metallocenes, the aluminohydride of zirconocene complex showed higher activity in solution than in suspension, however its thermal and kinetic stability was significantly increased. The effect of the co‐catalyst concentration (MAO) on the activity and the molecular weight of the polymers are also reported in this study, finding that in heterogeneous phase low concentrations of MAO were used to activate the pre‐catalyst. The MW of the polymers and copolymers synthesized with the supported Me3SiCp2ZrH3AlH2/SiO2 could be controlled by adding molecular hydrogen (H2) as chain transfer agent in the polymerization and copolymerization reactions.

Synthesis and Structural Analysis of Titanatranes Bearing Terminal Substituted Aryloxo Ligands of the type [Ti(OAr){(O-2,4-Me2C6H2-6-CH2)2(OCH2CH2)N}]n (n = 1, 2): Effect of Aryloxo Substituents in the Ethylene Polymerization

A series of titanatranes containing both chelate bis(aryloxo)-(alkoxo)amine and the terminal aryloxo ligands of type [Ti(OAr)(L)](n) [n = 1 or 2, Ar = 2,6-Me(2)C(6)H(3) (1), 2,6-(i)Pr(2)C(6)H(3) (2), 2,6-Ph(2)C(6)H(3) (3), 2-FC(6)H(4) (4), 2,6-F(2)C(6)H(3) (5), C(6)F(5) (6); L = (O-2,4-Me(2)C(6)H(2)-6-CH(2))(2)(OCH(2)CH(2))N)] have been prepared, and their structures (1, 3-6) were determined by X-ray crystallography. The ortho-substituents in the terminal aryloxo ligand directly affect the structure in the solid state; the structures of 1-3 possessed monomeric form and fold a distorted trigonal bipyramidal geometry around Ti, whereas the structure of 4-6 were of dimeric form and fold a distorted octahedral around Ti bridged with oxygen in the alkoxo arm expressed as [Ti(OAr){(O-2,4-Me(2)C(6)H(2)-6-CH(2))(2)(mu(2)-OCH(2)CH(2))N)}](2). The Ti-O(Ar) bond distances and the Ti-O-C(Ar) bond angles are highly influenced by the terminal aryloxo substituents especially in the ortho-position. The 2,6-(i)Pr(2)C(6)H(3) analogue (2), the C(6)F(5) analogue (6), and the 2,6-Me(2)C(6)H(3) analogue (1) showed moderate/notable catalytic activities for ethylene polymerization in the presence of MAO especially at 80-100 degrees C, whereas both the 2,6-Ph(2)C(6)H(3) analogue (3) and 2-FC(6)H(4) analogue (4) showed the negligible catalytic activities, clearly indicating that the activity was strongly affected by the terminal aryloxo substituents especially in the ortho-position.

Synthesis and Structural Analysis of Half-Titanocenes Containing η2-Pyrazolato Ligands, and Their Use in Catalysis for Ethylene Polymerization

Cp*TiCl(2)(L) [L = C(3)H(3)N(2) (1), 3,5-Me(2)C(3)HN(2) (2) and 3,5-(i)Pr(2)C(3)HN(2) (3)], and Cp*Ti(C(3)H(3)N(2))(3) (4) were prepared in moderate yields by treating Cp*TiCl(3) with the pyrazoles in the presence of Et(3)N or with their corresponding lithium salts in Et(2)O. The structures of 1 and 2 determined by X-ray crystallography indicate that these complexes fold a distorted tetrahedral geometry around Ti, and the pyrazolato ligands coordinate to Ti with eta(2)-N,N'-coordination mode. In contrast, one of the pyrazolato ligand in 4 coordinates to Ti with eta(1)-N-bonding, whereas the other two ligands were bound to Ti with eta(2)-N,N'-fashion. The Cp analogues, CpTiCl(2)(L) [L = C(3)H(3)N(2) (5), 3,5-Me(2)C(3)HN(2) (6), 3,5-(i)Pr(2)C(3)HN(2) (7), and 3,5-Ph(2)C(3)HN(2) (8)], were also prepared by the reaction of CpTiCl(3) with the corresponding lithium salts in Et(2)O or n-hexane. The crystallographic analyses of 5 and 6 revealed that the pyrazolato ligands coordinate to Ti with eta(2)-N,N'-coordination mode. These complexes (1-3, 5-8) exhibited moderate catalytic activities for ethylene polymerization in the presence of methylaluminoxane (MAO), and the activities were highly affected by the substituent on the pyrazolato ligand employed. Complex 1 exhibited the highest activity affording polymer with uniform molecular weight distribution, suggesting that the polymerization proceeded with uniform catalytically active species. An increase in the steric bulk in the pyrazolato ligand led to a slight decrease in the activity by the Cp* analogues, whereas the activity by the Cp analogues increased upon increasing the steric bulk in the pyrazolato ligand employed.

Tris(pyrazolyl)borate Ti(IV) Complexes Containing Phenoxy Ligands: Effective Catalyst Precursors for Ethylene Polymerization That Proceeds via Cationic Ti(IV) Species

A series of phenoxy-substituted tris(pyrazolyl)borate titanium complexes, Tp′TiCl2(OAr) and Tp*TiMe2(OAr) [Tp = HB(pyrazolyl)3, Tp* = HB(3,5-Me2-pyrazolyl)3; Ar = Ph, 2,6-Me2C6H3, 2,6-iPr2C6H3], were prepared, and their structures were determined by X-ray crystallography. These complexes exhibited from moderate to remarkable catalytic activities for ethylene polymerization in the presence of MAO; TpTiCl2(OPh) exhibited the highest catalytic activity for ethylene polymerization. The cationic Ti(IV)−methyl complex, [Tp*TiMe(O-2,6-Me2C6H3)]+[MeB(C6F5)3]−·(THF)2, polymerizes ethylene to give polyethylene with a uniform molecular weight distribution, clearly indicating that the cationic Ti(IV) species plays an essential role as the active species.

Scandium and yttrium complexes of a heteroscorpionate [N,N,O]-donor-set ligand: Synthesis, characterization and catalytic activity in ethylene polymerization

New scandium and yttrium complexes ScL 2( bpzmp)(THF) {L = Cl ( 1); L = CH 2Si(CH 3) 3 ( 3)}, YL 2( bpzmp) {L = Cl ( 2); L = OTf ( 5)} and Y(CH 2SiMe 3) 2( bpzmp)(THF) ( 4) bearing the heteroscorpionate bpzmp ligand { bpzmp = (3,5- t Bu 2-2-phenoxo)bis(3,5-Me 2-pyrazol-1-yl)methane} have been synthesized and characterized by means of NMR and Mass spectroscopy. The tridentate monoanionic ligand resulted κ 3-coordinated to the metal via the oxygen and both the sp 2 nitrogen atoms of the heterocycles, producing complexes in C S symmetry. The behavior of 1– 4 in ethylene polymerization was investigated after proper activation with different activating agents. Complex 4, in combination with the Brönsted or Lewis acids [PhNMe 2H][B(C 6F 5) 4] or [Ph 3C][B(C 6F 5) 4], produced linear high molecular weight polyethylene in good yield.

Ethylene polymerization and ethylene/1-octene copolymerization using group 4 half-metallocenes containing aryloxo ligands, Cp*MCl 2(OAr) [M = Ti, Zr, Hf; Ar = O-2,6-R 2C 6H 3, R = tBu, Ph]—MAO catalyst systems

Effect of the centered metal toward the catalytic activity as well as comonomer incorporation has been explored in ethylene (co)polymerization using a series of Cp*MCl 2(O-2,6-R 2C 6H 3) [M = Ti ( 1), Zr ( 2), Hf ( 3); R = Ph ( a), t Bu ( b), i Pr ( c)] in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 2a, 3a, b were prepared and identified, and the structures for 2–3a, b were determined by X-ray crystallography as a distorted tetrahedral geometry around the metal center. The catalytic activity in ethylene polymerization was affected by the centered metal employed [Ti > Zr > Hf]; the complexes containing 2,6-diphenylphenoxy ligand ( 1–3a) showed higher catalytic activities than the complexes containing 2,6-di- tert-butylphenoxy analogues ( 1–3b). The molecular weights in the resultant polymers prepared by the Zr and the Hf analogues were lower than those prepared by the Ti–Ph ( 1a) and the Ti– i Pr ( 1c) analogues. Although the copolymerizations of ethylene with 1-octene afforded the copolymers with uniform molecular weight distributions (except 1b), both the catalytic activities and the 1-octene incorporation were highly affected by the centered metal employed; the Ti– i Pr analogue ( 1c) seems to be the most suited in terms of both the catalytic activity and the 1-octene incorporation. The attempted copolymerization of ethylene with 2-methyl-1-pentene using 2a, b and 3a—MAO catalysts afforded linear polyethylene.

Copolymerization of ethylene with norbornene catalyzed by cationic rare earth metal fluorenyl functionalized N-heterocyclic carbene complexes

Rare earth metal bis(alkyl) complexes attached by fluorenyl modified N-heterocyclic carbene (NHC) (Flu-NHC)Ln(CH(2)SiMe(3))(2) (Flu-NHC = (C(13)H(8)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6); Ln = Sc (2a); Y (2b); Ho (2c); Lu (2d)), ((tBu)Flu-NHC)Ln(CH(2)SiMe(3))(2) ((tBu)Flu-NHC = 2,7-(t)Bu(2)C(13)H(6)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6; Ln = Sc (1a); Lu (1d)) and attached by indenyl modified N-heterocyclic carbene (Ind-NHC)Ln(CH(2)SiMe(3))(2) (Ind-NHC = C(9)H(6)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6; Ln = Sc (3a); Lu (3d)), under the activation of Al(i)Bu(3) and [Ph(3)C][B(C(6)F(5))(4)], showed varied catalytic activities toward homo- and copolymerization of ethylene and norbornene. Among which the scandium complexes, in spite of ligand type, exhibited medium to high catalytic activity for ethylene polymerization (10(5) g mol(Sc)(-1) h(-1) atm(-1)), but all were almost inert to norbornene polymerization. Remarkably, higher activity was found for the copolymerization of ethylene and norbornene when using Sc based catalytic systems, which reached up to 5 x 10(6) g mol(Sc)(-1) h(-1) atm(-1) with 2a. The composition of the isolated copolymer was varying from random to alternating according to the feed ratio of the two monomers (r(E) = 4.1, r(NB) = 0.013). The molecular structure of complex 1d was characterized by X-ray analysis. The influences of structural factors of complexes and polymerization conditions on both the catalytic activity and the norbornene content in the copolymer were discussed.

Zirconium and hafnium complexes supported by linked bis(β-diketiminate) ligands: synthesis, characterization and catalytic application in ethylene polymerization

Zirconium and hafnium complexes bearing new 1,2-ethanediyl- or 1,3-propanediyl-linked bis(beta-diketiminate) ligands, [{C(n)H(2n)-(BDI(Ar))(2)}MCl(2)] (Ar = 2,6-Me(2)-C(6)H(3), 2,6-Cl(2)-C(6)H(3), 2,6-(i)Pr(2)-C(6)H(3); M = Zr, n = 2 (4a-c), n = 3 (5a-c); M = Hf, n = 2 (6b)), were synthesized via the reaction of MCl(4).2THF and one equivalent of dilithium salt of the corresponding ligand. Distorted trigonal prismatic and octahedral coordination geometries as well as C(1)-symmetric structures are found for zirconium complexes and in the solid state. Variable temperature (1)H NMR spectra indicated the fluxional nature of and in solution. Upon activation with methylaluminoxane (MAO), all these complexes except hafnium complex displayed moderate catalytic activities for ethylene polymerization. 1,2-Ethanediyl-linked complexes and are generally more active than their 1,3-propanediyl-linked analogues. The substituents at the ortho-positions of the phenyl rings have different effect on the catalytic activities of 1,2-ethanediyl-linked series or 1,3-propanediyl-linked series. It is noteworthy that even at a low Al/Zr molar ratio of 500, the catalytic activities of these zirconium complexes could be retained. Polyethylenes with broad molecular weight distributions (MWD = 15.3-20.3) were produced, which might result from the fluxional character of the zirconium complexes. The linear structure of obtained polyethylenes was further determined by (13)C NMR spectroscopy and DSC analysis.

Imino‐indolate half‐titanocene chlorides: Synthesis and their ethylene (co‐)polymerization

AbstractA series of imino‐indolate half‐titanocene chlorides, Cp′Ti(L)Cl2 (C1–C7: Cp′ = C5H5, MeC5H4, C5Me5, L = imino‐indolate ligand), were synthesized by the reaction of Cp′TiCl3 with sodium imino‐indolates. All complexes were characterized by elemental analysis, 1H and 13C NMR spectroscopy. Moreover, the molecular structures of two representative complexes C4 and C6 were confirmed by single crystal X‐ray diffraction analysis. On activation with methylaluminoxane (MAO), these complexes showed good catalytic activities for ethylene polymerization (up to 7.68 × 106 g/mol(Ti)·h) and ethylene/1‐hexene copolymerization (up to 8.32 × 106 g/mol(Ti)·h), producing polyolefins with high molecular weights (for polyethylene up to 1808 kg/mol, and for poly(ethylen‐co‐1‐hexene) up to 3290 kg/mol). Half‐titanocenes containing ligands with alkyl substituents showed higher catalytic activities, whereas the half‐titanocenes bearing methyl substituents on the cyclopentadienyl groups showed lower productivities, but produced polymers with higher molecular weights. Moreover, the copolymerization of ethylene and methyl 10‐undecenoate was demonstrated using the C1/MAO catalytic system. The functionalized polyolefins obtained contained about 1 mol % of methyl 10‐undecenoate units and were fully characterized by several techniques such as FT‐IR, 1H NMR, 13C NMR, DSC, TGA and GPC analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 357–372, 2009

Synthesis and Structural Analysis of (Cyclopentadienyl)(pyrrolide)titanium(IV) Complexes and Their Use in Catalysis for Olefin Polymerization

Cp*TiCl2(L) [L = C4H4N (1), 2,5-Me2C4H2N (2), 2,4-Me2C4H2N (3), 2,4-Me2-3-EtC4HN (4)], Cp*TiCl(2,4-Me2-3-EtC4HN)2 (5), and Cp*Ti(C4H4N)3 (6) were prepared by treating Cp*TiCl3 with the corresponding lithium salts in toluene or n-hexane. The structures of 3−6 determined by X-ray crystallography indicate that the complexes have a distorted tetrahedral geometry around Ti, and the nitrogen atom binds to Ti in an η1 fashion. The dimethyl analogues Cp*TiMe2(L) [L = C4H4N (7), 2,5-Me2C4H2N (8)] could be prepared by adopting a route that involves in situ generation of Cp*Ti(Cl)Me2, prepared by the reaction of Cp*TiCl3 with 2.0 equiv of MeLi in Et2O, and the subsequent treatment with the corresponding lithium salts. The Cp analogues CpTiCl2(L) [L = C4H4N (9), 2,5-Me2C4H2N (10), 2,4-Me2C4H2N (11), 2,4-Me2-3-EtC4HN (12)] were also prepared by treating CpTiCl3 with the corresponding lithium salts in Et2O or n-hexane. The crystallographic analyses of 9−11 indicate that the dimethylpyrrolide ligand in 10 coordinates to Ti in η5 mode, whereas the nitrogen atom in the pyrrolide ligand (in complexes 9 and 11) binds to Ti in an η1 fashion (σ bonding in addition to π donation). These complexes (1−4, 7−12) exhibited moderate catalytic activities for ethylene polymerization in the presence of methylaluminoxane (MAO), and the activities were highly affected by the substituent on the pyrrolide ligand. In the polymerization using a series of dichloro complexes, the Cp*-pyrrolide analogue 1 exhibited the highest catalytic activity, and an increase in the steric bulk led to the decrease in activity, whereas the activity of the Cp analogues increased upon increasing the steric bulk in the pyrrolide ligand. The dimethyl complexes (7, 8) exhibited notable catalytic activities in the presence of MAO, and the activities increased in the presence of iBu3Al/[Ph3C][B(C6F5)4] cocatalyst in place of MAO. The resultant polymers possessed unimodal molecular weight distributions. These complexes also exhibited moderate catalytic activities for syndiospecific styrene polymerization, and the activities of the Cp* analogues increased at high temperature.

Synthesis and Characterization of Titanium Complexes Bearing Two β-Enaminoketonato Ligands with Electron-Withdrawing Groups and Their Behavior in Ethylene Polymerization

A series of new titanium complexes with two asymmetric bidentate β-enaminoketonato (N,O) ligands (4b−t), [RN═C(CF3)CHC(t-Bu)O]2TiCl2 (4b, R = −C6H4F(o); 4c, R = −C6H4F(m);4d, R = −C6H4F(p); 4e, R = −C6H3F2(2,3); 4f, R = −C6H3F2(2,4); 4g, R = −C6H3F2(2,5); 4h, R = −C6H3F2(2,6); 4i, R = −C6H3F2(3,4); 4j, R = −C6H3F2(3,5); 4k, R = −C6H2F3(2,3,4); 4l, R = −C6H2F3(3,4,5); 4m, R = −C6H4CF3(o); 4n, R = −C6H4CF3(m); 4o, R = −C6H4CF3(p); 4p, R = −C6H4Cl(p); 4q, R = −C6H4I(p); 4r, R = −C6H4NO2(p); 4s, R = −CH2C6H5; 4t, R = −C6H11), have been synthesized and characterized. X-ray crystal structures suggest that complexes 4a−d, 4j, and 4m all adopt a distorted octahedral geometry around the titanium centers. Two chlorine atoms in complexes 4a−d and 4j are in cis-configuration, while those of complex 4m are trans. NMR spectra and X-ray structure analyses reveal that the conformational isomers of some complexes, such as 4b, in which the two β-enaminoketonato ligands bear asymmetrical N-phenyl rings, exist both in solution and in solid state. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4b−l and 4n−q are highly active toward ethylene polymerization and produce high molecular weight polyethylenes. The catalytic activities are significantly enhanced by introducing electron-withdrawing groups (EWG), such as fluorine and chlorine atom(s) or the trifluoromethyl group, into suitable positions on the N-aryl rings. The titanium complex 4m is inactive toward ethylene polymerization due to the trans-configuration of the two chlorine atoms. In addition, the titanium complexes display low catalytic activity for ethylene polymerization only if the N-substituents are not aromatic.

Synthesis and Structural Analysis of (Arylimido)vanadium(V) Complexes Containing Phenoxyimine Ligands: New, Efficient Catalyst Precursors for Ethylene Polymerization

A series of (arylimido)vanadium(V) complexes containing phenoxyimine ligands of the type V(NAr)Cl2[O-2-R-6-{(2,6-iPr2C6H3)N═CH}C6H3] [Ar = 2,6-Me2C6H3; R = H (1a), Me (1b), tBu (1c)] have been prepared in 64−78% yields from V(NAr)Cl3 with LiO-2-R-6-[(2,6-iPr2C6H3)N═CH]C6H3. The structures for 1a−c determined by X-ray crystallography indicate that these complexes have distorted square-pyramidal structures around vanadium, consisting of the arylimido ligands in the apical site of a distorted square-pyramid and the N,O-chelate ligand, which forms a plane including both the aryloxo ring and the imino nitrogen. The Cl−V−Cl bond angle for 1c [90.49(2)°] is apparently smaller than those in 1a,b [91.97(7)°, 91.25(2)°, respectively], and the V−N(imine) bond distance in 1c [2.203(2) A] is shorter than those in 1b,c [2.216(4), 2.2165(17) A, respectively]. These complexes (especially 1c) exhibited notable catalytic activities for ethylene polymerization in the presence of MAO, and the ortho substituent in the aryloxo...

Half‐titanocene complexes bearing dianionic 6‐benzimidazolylpyridyl‐2‐carboximidate ligands: Synthesis, characterization, and their ethylene polymerization

Abstract6‐Benzimidazolylpyridyl‐2‐carboximidic half‐titanocene complexes, Cp′TiLCl (Cp′ = C5H5, MeC5H4, C5Me5, L = 6‐benzimidazolylpyridine‐2‐carboxylimidic, C1–C13), were synthesized and characterized along with single‐crystal X‐ray diffraction. The half‐titanocene chlorides containing substituted cyclopentadienyl groups, especially pentamethylcyclopentadienyl groups were more stable, while those without substituents on the cyclopentadienyl groups were easily transformed into their dimeric oxo‐bridged complexes, (CpTiL)2O (C14 and C15). In the presence of excessive amounts of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all half‐titanocene complexes showed high catalytic activities for ethylene polymerization. The substituents on the Cp groups affected the catalytic behaviors of the complexes significantly, with less substituents favoring increased activities and higher molecular weights of the resultant polyethylenes. Effects of reaction conditions on catalytic behaviors were systematically investigated with catalytic systems of mononuclear C1 and dimeric C14. With C1/MAO, large MAO amount significantly increases the catalytic activity, while the temperature only has a slight effect on the productivity. In the case of C14/MAO catalytic system, temperature above 60 °C and Al/Ti value higher than 5000 were necessary to observe good catalytic activities. In both systems, higher reaction temperature and low cocatalyst amount gave the polyethylenes with higher molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3396–3410, 2008